1. Field of the Invention
This invention relates to cone type lock washers for use with headed bolts and in particular to cone type lock washers having means to indicate that a tension within a predetermined range of tensions has been realized in a bolt.
2. The Prior Art
Controlling the amount of tension in a bolt is often a critical parameter in various assembly operations. If a bolt is not tight enough (i.e. if the bolt is undertensioned), the joint of which the bolt as a member may not be as strong as required and/or the bolt may further loosen under the effects of vibration and the like. On the other hand, if the bolt is tighter than desired (i.e. if the bolt is overtensioned), the bolt may be over stressed and subject to failure.
One prior art technique for controlling the tension in a bolt to a predetermined tension, or range of tensions, was to attempt to control the torque at which the bolt, or a nut associated therewith, was tightened. This method is not totally satisfactory as the control of applied torque by manual and/or automatic methods is difficult, torque indicating or limiting tools may not be available, and further as the correlation of applied torque to tension is often subject to large variations.
Other methods to control tension in bolts have involved washers or bolt heads which were designed to deform or otherwise indicate that a predetermined axial compression had to be applied thereto which compression equalled the tension in the bolt. Such methods generally provided an accurate indication of tension, but were not totally satisfactory as the washers or bolt heads were complicated and/or expensive to produce, indicated only one of either an over or under tension condition, required visual inspection, required extensive redesign to modify the torque indicated, required the washer to be substantially flattened and/or were not suitable for reuse as a lock washer.